FIG. 1 depicts a conventional method 10 for fabricating a read transducer that uses soft magnetic biasing. The method 10 starts after the first shield has been provided and the layers for the sensor are deposited. The sensor is defined in the track width direction, via step 12. Step 12 typically includes providing a first mask that covers the desired portion of the sensor layers in the track width direction and milling the exposed portions of the sensor layers. In addition, an insulating layer may be deposited. The soft bias layer is deposited, via step 14. The insulating layer electrically insulates the sensor from the soft bias material(s). The first mask may then be removed.
The read sensor is then masked and partially milled through, via step 16. The first conventional milling mask used in step 16 sets the stripe height of the free layer. The stripe height of the free layer is the distance the free layer extends from the ABS in a direction perpendicular to the ABS. The soft bias layer is also milled in step 16. The mask used in step 16 is substantially rectangular in shape and covers both the sensor and the soft bias layer. Both the soft bias layer and the sensor are partially milled through. Thus, the unmilled portion of the soft bias layer and the free layer have substantially the same stripe height. Once the read sensor is milled to the desired depth, step 16 terminates and the first conventional milling mask is removed.
A second conventional milling mask is provided and the remaining portion of the sensor layers and the soft bias layers are milled, via step 18. In step 18, the stripe height of the pinned layer is set. The conventional second milling mask used in step 18 is also rectangular in shape, but typically extends further from the ABS than the first conventional milling mask. As a result, the pinned layer extends further from the ABS than the free layer. The second conventional milling mask covers some portion of the soft bias layer. As a result, an exposed portion of the soft bias layer continues to be milled, but a covered portion is not. Once step 18 is completed, the second conventional milling mask is removed. The second shield is then deposited in step 20.
FIGS. 2A-2C depict an air-bearing surface (ABS) and side views of a conventional read transducer 50 which utilizes soft bias structures. The conventional read transducer 50 includes shields 52 and 58, sensor 54, soft bias structures 56. The read sensor 54 is typically a giant magnetoresistive (GMR) sensor or tunneling magnetoresistive (TMR) sensor. The read sensor 54 includes an antiferromagnetic (AFM) layer, a pinned layer, a nonmagnetic spacer layer, and a free layer, which are not shown for simplicity. Also shown is a capping layer. In addition, seed layer(s) may be used. The free layer has a magnetization sensitive to an external magnetic field. Thus, the free layer functions as a sensor layer for the magnetoresistive sensor 54. Consequently, as used herein a sensor layer is typically a free layer. The soft bias structures 56 are used to magnetically bias the sensor layer of the sensor 54.
As can be seen in FIG. 2B, the conventional free layer of the conventional sensor 58 has a first stripe height, h1. This height is on the order of forty to fifty nanometers. This stripe height h1 was formed in step 16. The conventional extended pinned layer has a greater stripe height, h2. The second stripe height h2 of the extended pinned layer is defined in step 18. The conventional soft bias structures 56 extend to the second shield 58 and have a stripe height h1. The conventional soft bias structures 56 are defined in step 16.
Although the conventional transducer 50 functions, there are drawbacks. After fabrication is complete, residue 57 from the soft bias layer deposited in step 14 still remains. The residue 57 is present because the soft bias layer and sensor are not completely milled through in step 16. The residue is thus prevented from being milled by the mask used in step 18. The residue 57 is magnetically connected to the adjoining conventional soft magnetic bias structure 56. The conventional soft bias structures 56 are connected to the conventional shield 58. However, the conventional soft bias structures 56 extend only to h1, which is typically on the order of forty nanometers. Further, the residue 57 does not extend to the shield 58. The residue 57 is thus not stabilized by the shield 58. The residue 57 is thus magnetically unstable. Such instabilities adversely affect reliability of the conventional read transducer 50.
Accordingly, what is needed is a system and method for improving the reliability of a magnetic recording read transducer.